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[DPRG] FW: Any ideas?

Subject: [DPRG] FW: Any ideas?
From: Mike McCarty jmccarty at ssd.usa.alcatel.com
Date: Wed Oct 11 10:18:39 CDT 2000

On Tue, 10 Oct 2000, RoboVac wrote:

> The standard method for increasing the range of photoelectric sensors for
> this sort of application is to pulse the beam.  To do this first measure the
> amount of returned light with the light turned off.  Then measure the amount
> of returned light with the light turned on.
> Subtracting the two values removes the effects of room lights, sun shine,
> etc.  Because of the removal of the noise from any external lights the
> signal to noise ratio is higher and the sensor works at longer distances.
> The same technique can be used for a laser sensor also.  However not all
> laser can be pulsed in this manner.  Most of the lasers used in laser
> pointers need to be left on for longer then the standard 40kHz or they do
> not emit any light.

Some may be damaged by rapid pulsing. One possibility is not to use
electronic but rather electromechanical means for modulating the light.
One possibility (which works to the 10s of KHz at least) is to put the
signal out to a small speaker with a reflector mounted on it, and
bounce the light off of the reflector.

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